Immunization of tumor-bearing hosts with Vibrio cholerae neuraminidase (NANAase)-treated tumor cells alone or in combination with chemotherapy slows the growth or causes regression of established tumors. Although this type of immunotherapy has been explored in a number of animal models and has been used in man, information is lacking on why NANAase treatment enhances immunogenicity. We have developed a chemoimmunotherapy model for treating L1210 ascites tumors in DBA/2J mice by combining 1-(2-chloroethyl)-3-(4-methylcyclohexyl)-1-nitrosurea (MeCCNU) with NANAase-treated purified L1210 plasma membranes. Because the immunogen is a purifed subcellular particle of known protein and glycoprotien composition, we can analyze at the molecular level the NANAase modifications of the membranes and how these affect the immune response to the tumor. We will use two-dimensional immunoelectrophoresis to analyze the immune response of DBA/2J mice to NANAase-treated L1210 plasma membranes to determine the relationship between glycoproteins modified by NANAase and the antigens to which the host responds. We will also determine whether the plasma membranes of tumor cells surviving chemotherapy are more closely related to NANAase-treated membranes prepared from the parent tumor than to untreated membranes from that tumor. This will be done by producing an L1210 tumor line resistant to MeCCNU chemotherapy and by using biochemical and immunochemical techniques to compare its plasma membranes with those of NANAase-treated and untreated membranes of the parent tumor. In addition, we will study the role in the immune response to NANAase-modified membranes of naturally occurring serum factors that recognize determinants on NANAase-treated cells; we will determine whether modified membranes are more effective in animals preimmunized to increase the level of these factors or whether modified membranes preincubated with serum containing these factors are more effective than those that have been preincubated.